Ethylene/propylene copolymer rubbers

Abstract: A process for the production of EPRs comprising contacting ethylene, propylene, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: a vanadium compound; a modifier; and a support, wherein said catalyst precursor has been pre-oxidized with an oxidant in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) a cocatalyst; and, (C) optionally, a promoter.

Description: Technical Field This invention relates to a process for the production of ethylene/propylene copolymer rubbers (EPRs), which include ethylene/propylene copolymers (EPMs) and ethylene/propylene/ethylidene norbornene terpolymers (EPDMs), generally having a crystalline content of less than 15 percent by weight. Background of Information The EPRs are elastomeric copolymers and terpolymers used in such applications as hose and tubing, wire and cable, gaskets, and single ply roofing. They are usually formulated with fillers, oils, processing aids, and stabilizing agents, and cured by reacting the polymers with sulfur in the presence of accelerators or with a combination of sulfur and an organic peroxide such as dicumyl peroxide. These polymers are presently manufactured commercially in solution and slurry processes with soluble vanadium catalysts. These processes are very expensive to run, requiring solvent removal and steam stripping steps. In addition, these solution catalysts do not provide satisfactory particle morphology in a fluidized bed. Improvement in these processes would be desirable and, particularly, the development of a gas phase process to produce these same products would be more economically attractive because little post-reaction cost will be incurred, and particle morphology would, expectedly, be improved. One of the catalysts selected to produce the EPRs in the gas phase is described in United States patent 4,508,842. Typically, the catalyst is comprised of a catalyst precursor, which is the reaction product of vanadium trichloride and an electron donor, the precursor being reacted with an aluminum containing modifier, and impregnated into a silica support; a promoter such as chloroform; and a triisobutylaluminum cocatalyst. This catalyst does achieve good particle morphology, but poor overall product, e.g., EPRs made with this catalyst exhibit poor cure and contain much high temperature crystallinity. This is believed to be the result of poorly distributed propylene, and, in the case of the EPDMs, poorly distributed diene. Adjustments with respect to the cocatalyst and the promoter were found to improve the propylene distribution and lower the high temperature crystallinity, but only a marginal improvement in the cure was achieved. Disclosure of the Invention An object of this invention, therefore, is to provide a process for the production of EPRs having a high cure performance. Other objects and advantages will become apparent hereinafter. According to the present invention, the above object is met by a process for the production of EPRs comprising contacting ethylene, propylene, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX 3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX 3 is soluble; (ii) a modifier having the formula BX 3 or AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is as defined above; and a is 1 or 2; and (iii) a support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with a sufficient amount of oxidant to increase the oxidation state of the vanadium by at least one; (B) a cocatalyst consisting essentially of a compound having the formula AlR (3-a) X a and, optionally, a compound having the formula AlR 3 wherein R, X, and a are as defined above; and, (C) optionally, a promoter, which is a chlorinated ester having at least 2 chlorine atoms; a saturated or unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms; or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms. Description of the Preferred Embodiment(s) The vanadium based catalyst and a process for preparing same are described in United States patent 4,508,842. The preferred vanadium trihalide (VX 3 ) is vanadium trichloride. The electron donor is a liquid, organic Lewis base in which the vanadium trihalide is soluble. It is, generally, liquid at temperatures in the range of 0°C to 200°C. The electron donor can be an alkyl ester of an aliphatic or aromatic carboxylic acid, an aliphatic ketone, an aliphatic amine, an aliphatic alcohol, an alkyl or cycloalkyl ether, or mixtures thereof, each electron donor having 2 to 20 carbon atoms. Among these electron donors, the preferred are alkyl and cycloalkyl ethers having 2 to 20 carbon atoms; dialkyl, diaryl, and alkylaryl ketones having 3 to 20 carbon atoms; and alkyl, alkoxy, and alkylalkoxy esters of alkyl and aryl carboxylic acids having 2 to 20 carbon atoms. The most preferred electron donor is tetrahydrofuran. Other examples of suitable electron donors are methyl formate, ethyl acetate, butyl acetate, ethyl ether, dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methyl acetate, ethyl anisate, ethylene carbonate, tetrahydropyran, and ethyl propionate. While an excess of electron donor is used initially to provide the reaction product of vanadium compound and electron donor, the reaction product finally contains 1 to 20 moles of electron donor per mole of vanadium compound and preferably 1 to 10 moles of electron donor per mole of vanadium compound. The modifier has the formula BX 3 or AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is independently chlorine, bromine, or iodine; and a is 1 or 2. One or more modifiers can be used. Preferred modifiers include alkylaluminum mono- and dichlorides wherein each alkyl radical has 1 to 6 carbon atoms; boron trichloride; and the trialkylaluminums. From 0.1 to 10 moles, and preferably from 0.2 to 2.5 moles, of modifier can be used per mole of electron donor. The molar ratio of modifier to vanadium can be in the range of from 1:1 to 10:1 and is preferably in the range of from 2:1 to 5:1. The promoter can be a chlorinated ester having at least 2 chlorine atoms or a perchlorinated ester. Suitable esters are Cl 3 CCOOC 2 H 5 (ethyl trichloroacetate); Cl 3 CCOOCH 3 (methyl trichloroacetate; CCl 3 CCl= CClCOOC 4 H 9 ; C 6 H 5 CCl 2 COOR wherein R is an alkyl radical having 1 to 8 carbon atoms; and Cl 2 C= CCl-CCl 2 COOC 4 H 9 . The promoter can also be a saturated aliphatic halocarbon having the formula C 3 (X) a (F) b (H) c wherein each X is independently chlorine, bromine, or iodine; a is an integer from 6 to 8; b and c are integers from 0 to 2; and a+b+c equal 8. Examples of these halocarbon promoters are hexachloropropane, heptachloropropane, and octachloropropane. These saturated halocarbon promoters are mentioned in United States patent 4,892,853. In addition, the promoter can also be an unsaturated aliphatic halocarbon such as perchloropropene or any unsaturated halocarbon having a CX 3 group attached to a C= C group wherein each X is independently chlorine, bromine, or iodine, or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms such as trichlorotoluene and trichloroxylene. Again, the halogen can be chlorine, bromine, or iodine.The number of carbon atoms in the halocarbon or the haloalkyl substituent can be 1 to 14, and the number of benzene rings in the halocarbon or the aromatic hydrocarbon can be 1 to 3, but is preferably one. From 0.01 to 10 moles, and preferably from 0.1 to 2 moles, of promoter can be used per mole of cocatalyst. The cocatalyst can be a compound having the formula AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is independently chlorine, bromine, or iodine; and a is 1 or 2 or a mixture of compounds having the formulas AlR (3-a) X a and AlR 3 wherein R, X, and a are the same as above. The molar ratio of the alkylaluminum halide to the trialkylaluminum, if used, can be at least 0.5:1, and is preferably in the range of from 2.0:1 to 2.5:1. The total cocatalyst can be present in the catalyst system in an amount of from 10 to 500 moles of cocatalyst per gram atom of vanadium, and is preferably introduced in an amount of from 30 to 150 moles of cocatalyst per gram atom of vanadium. Examples of halogen containing modifiers and cocatalysts are diethylaluminum chloride; ethylaluminum sesquichloride; di-n-butylaluminum chloride; diisobutylaluminum chloride; methylaluminum sesquichloride; isobutylaluminum sesquichloride; dimethylaluminum chloride; di-n-propylaluminum chloride; methylaluminum dichloride; and isobutylaluminum dichloride. Examples of hydrocarbyl cocatalysts are as follows: triisobutylaluminum, trihexylaluminum, di-isobutylhexylaluminum, isobutyl dihexyl-aluminum, trimethylaluminum, triethylaluminum, tripropylaluminum, triisopropylaluminum, tri-n-butylaluminum, trioctylaluminum, tridecylaluminum, and tridodecylaluminum. Preferred hydrocarbyl cocatalysts are triethylaluminum, triisobutylaluminum, and trihexylaluminum. The support can be inorganic or organic such as silica, alumina, or polymeric; silica is preferred. Examples of polymeric supports are a porous crosslinked polystyrene and polypropylene. A typical silica or alumina support is a solid, particulate, porous material essentially inert to the polymerization. It is used as a dry powder having an average particle size of from 10 to 250 microns and preferably from 30 to 100 microns; a surface area of at least 200 square meters per gram and preferably at least about 250 square meters per gram; and a pore size of at least 100 angstroms and preferably at least 200 angstroms. Generally, the amount of support used is that which will provide from 0.1 to 1.0 millimole of vanadium per gram of support and preferably from 0.4 to 0.9 millimole of vanadium per gram of support. Impregnation of the above mentioned catalyst precursor into a silica support is accomplished by mixing the precursor and silica gel in the electron donor solvent or other solvent followed by solvent removal under reduced pressure. The modifier is usually dissolved in an organic solvent such as isopentane and impregnated into the support following impregnation of the precursor, after which the supported catalyst precursor is dried. The promoter can also be impregnated into the support in similar fashion, if desired. The cocatalyst and promoter are preferably added separately neat or as solutions in an inert solvent, such as isopentane, to the polymerization reactor at the same time as the flow of ethylene is initiated. As noted above, the catalyst precursor or prepolymerized catalyst precursor is pre-oxidized with a sufficient amount of oxidant to raise the valence or oxidation state of the vanadium by at least one. This is accomplished after the catalyst precursor or prepolymerized catalyst precursor is formed, but before the precursor is introduced into the reactor where the polymerization is to take place. Thus, the catalyst precursor, which comprises the reaction product of a vanadium trihalide and an electron donor impregnated into a support and further reacted, within the support, with a modifier, and which may be in the prepolymerized state is further subjected to oxidation with an oxidant such as oxygen; nitrobenzene, para-nitrotoluene, ortho-nitrotoluene, nitromethane, and nitroethane; a functionalized, unsaturated halocarbon compound (preferably a strong chlorinated oxidant) exemplified by perchloropropene or any unsaturated perchlorinated hydrocarbon having at least 3 carbon atoms, and hexachlorocyclopentadiene; and a saturated halocarbon having the formula C 3 (X) a (F) b (H) c wherein each X is independently chlorine, bromine, or iodine; a is an integer from 6 to 8; b and c are integers from 0 to 2; and a+b+c equal 8. Examples of these saturated halocarbon oxidants are hexachloropropane, heptachloropropane, and octachloropropane. These saturated halocarbons are referred to in United States patent 4,892,853, mentioned above in connection with the promoters. In addition, the oxidant can be an aromatic halocarbon such as trichlorotoluene, trichlorobenzene, and trichloroxylene. The oxidation is typically carried out by admixing the catalyst precursor with an inert hydrocarbon diluent such as hexane; introducing the mixture into a reactor; adding the oxidant, usually in excess (but at least one mole of oxidant per gram atom of vanadium); heating the mixture to about 50° C for about 60 minutes; removing the diluent under reduced pressure; and isolating the dried oxidized catalyst precursor. The oxidation process is conducted under an inert atmosphere such as nitrogen. The vanadium oxidation state can be measured by direct KMnO 4 titration in 10 percent aqueous phosphoric acid. In the case of oxygen, the pre-oxidation can be accomplished without a diluent. The catalyst precursor described above can be used in prepolymer form. In this case, however, the prepolymerized catalyst precursor is subjected to the oxidation process rather than the catalyst precursor per se. A technique for prepolymerization can be found in United States patent 4,970,279. Typically, the prepolymerization is carried out in the liquid phase in a similar manner to a diluent slurry polymerization. The catalyst system used in the prepolymerization is the same one that will be used in the fluidized bed polymerization. The difference lies in the monomers used and weight ratio of monomer(s) to catalyst precursor, which is at least 10:1, and is typically 50:1 to 300:1. It should be pointed out that the numbers vary with the particular catalyst system selected. Examples of suitable prepolymers are homoprepolymers of ethylene, ethylene/propylene coprepolymers, ethylene/1-hexene coprepolymers, ethylene/propylene/1-hexene terprepolymers, and ethylene/propylene/diene terprepolymers. The prepolymer does not have to be the same as the resin product of the main polymerization. The amount of prepolymer formed, in terms of grams of prepolymer per gram of catalyst precursor, generally depends on the composition of the prepolymer, the composition of the polymer being produced, and the productivity of the catalyst employed. The prepolymer loading is chosen so as to minimize prepolymer residue in the product resin. When using ethylene homoprepolymers or ethylene/propylene coprepolymers, prepolymer loading can be in the range of from 10 to 500 grams of prepolymer per gram of catalyst precursor and is preferably in the range of from 50 to 300 grams of prepolymer per gram of catalyst precursor. A typical prepolymerization can be carried out in a slurry prepolymerizer. The equipment includes a monomer feed system, a reaction vessel, and an inert screener. The reactor is a jacketed pressure vessel with a helical ribbon agitator to give good solids mixing, and with a bottom cone to facilitate solids discharge. Ethylene is fed from cylinders, with the pressure regulated, through 4A or 13X molecular sieves to remove impurities, and then through a flow meter to measure flow rate. Other olefins, if required, are fed from cylinders via a dip tube with nitrogen pressure supplied to the cylinder headspace. They also pass through 4A or 13X molecular sieves and through a flow meter. The monomers can be fed to either the reactor headspace or subsurface, with subsurface preferred as it increases the reaction rate by eliminating one mass transfer step. Temperature is controlled with a closed loop tempered water system. Pressure is controlled with a vent/make-up system. The finished prepolymerized catalyst is screened to remove skins, agglomerates, and other types of oversize particles that could cause feeding difficulties into the gas phase reactor. The screening is done with a vibratory screener with a 20 mesh screen. The screener is kept under a nitrogen atmosphere to maintain the prepolymerized catalyst activity. Oversize material is collected for disposition. The desired undersize fraction is discharged into a cylinder for storage and shipping. The typical prepolymerization is a slurry polymerization of ethylene and, optionally, a comonomer under mild conditions. Isopentane, hexane, and heptane can be used as the solvent, with isopentane preferred for its higher volatility. Mild conditions are necessary to minimize catalyst decay during the prepolymerization so that there is sufficient activity for the subsequent gas phase polymerization, which may occur months after the prepolymerization. Such conditions will vary with different catalyst systems, but are typically temperatures of from 25 to 70°C, monomer partial pressures of from 103.35 to 275.6 kPa (15 to 40 psi), and levels of cocatalyst and catalyst promoter of from 1 to 5 moles per mole of vanadium. The prepolymer loading ranges from 10 to 500 grams per gram of supported catalyst precursor, preferably from 50 to 300 grams per gram. The comonomer content of the prepolymer ranges from 0 to 15 weight percent. Hydrogen, or other chain transfer agents, can be added at the start of polymerization or throughout the polymerization to control molecular weight. Additional olefins or dienes may also be added. When the polymerization is complete, the agitator is stopped and the solids are allowed to settle so that the excess solvent can be removed by decanting. The remaining solvent is removed by drying, using low temperatures to avoid catalyst decay. The dried prepolymer catalyst is discharged to a storage cylinder through an inert screener, to remove oversize (+20 mesh) material. The polymerization can be conducted in a solution or in a slurry as described above for the prepolymerization, or in the gas phase, preferably in a fluidized bed made up of particulate EPM or EPDM. The fluidized bed can be a stirred fluidized bed reactor or a fluidized bed reactor, which is not stirred. In terms of the fluidized bed, a superficial velocity of from 0.305 to 1.37 metres per second (1 to 4.5 feet per second) and preferably from 0.46 to 1.07 metres per second (1.5 to 3.5 feet per second) can be used. The total reactor pressure can be in the range of from 1134.82 kPa to 4235.32 kPa (150 to 600 psia) and is preferably in the range of from 1823.82 to 3546.32 kPa (250 to 500 psia). The ethylene partial pressure can be in the range of from 172.25 to 2411.5 kPa (25 psi to about 350 psi) and is preferably in the range of from 551.2 to 1722.5 kPa (80 psi to 250 psi). The temperature can be in the range of from 0° to 100°C. The gaseous feed streams of ethylene, propylene, and hydrogen (or another chain transfer agent) are preferably fed to the reactor recycle line while liquid ethylidene norbornene or another diene, if used, and the cocatalyst solution are preferably fed directly to the fluidized bed reactor to enhance mixing and dispersion. The prepolymer containing the catalyst precursor is transferred into the fluidized bed from the catalyst feeder. The composition of the EPM or EPDM product can be varied by changing the propylene/ethylene molar ratio in the gas phase and the diene concentration in the fluidized bed. The product is intermittently discharged from the reactor as the bed level builds up with polymerization. The production rate is controlled by adjusting the catalyst feed rate. The molar ratio of monomers in the reactor will be different for different catalyst systems, as is well-known to those skilled in the art. The propylene/ethylene molar ratio is adjusted to control the level of propylene incorporated into the terpolymer. For the vanadium catalyst described above, a range of from 0.35:1 to 3:1 is preferred. The hydrogen/ethylene molar ratio is adjusted to control average molecular weights of the terpolymer. For the catalyst system, a range of from 0.001:1 to 0.3:1 is preferred. The level of diene in the bed, if used, is in the range of from 1 to 15 weight percent based on the weight of the bed, and is preferably in the range of from 2 to 10 weight percent. Examples of useful dienes, in addition to ethylidene norbornene (ENB), are 1,4-hexadiene and dicyclopentadiene dimer. Steps can be taken to reduce agglomeration. For example, fluidization aids can be provided as described in United States patent 4,994,534. Also, the product discharge line between the reactor and the product pot is often plugged up with chunks between intervals of product drops. A continuous purge flow of nitrogen in the line prevents the plugging problem. Also, coating the reactor surface with a low surface energy material is shown to be beneficial to slow down the rate of fouling build up. In addition, control of the electrostatic level in the bed prevents static induced particle agglomeration. Static can be adjusted to a satisfactory level by controlled use of reaction rate, quick change of gas composition, selective use of static-neutralizing chemicals, and surface passivation with aluminum alkyls. Static can also be controlled by using small amounts of an inert conductive particulate material such as carbon black. The amount of inert particulate material is that which is sufficient to control static, i.e., from 0.5 to 1.5 percent by weight based on the weight of the fluidized bed. Carbon black is the preferred antistatic material. The mean particle size of the inert conductive particulate material is in the range of from 0.01 to 150 microns, preferably to about 10 microns. The mean particle size can refer to the particle per se or to an aggregate as in the case of carbon black. The carbon black materials employed can have a primary particle size of from 10 to 100 nanometers and an average size of aggregate (primary structure) of from 0.1 to 10 microns. The surface area of the carbon black can be from 30 to 1500 square meters per gram and can display a dibutylphthalate (DBP) absorption of from 80 to 350 cubic centimeters per 100 grams. It is preferred to treat the particulate material prior to its introduction into the reactor to remove traces of moisture and oxygen. This can be accomplished by purging the material with nitrogen gas, and heating using conventional procedures. Other antistatic agents are also found to be effective in keeping the static level under control as mentioned, for example, in United States patent 5,194,526. The residence time of the mixture of comonomers, resin, catalyst, and liquid in the fluidized bed can be in the range of from 1.5 to 8 hours and is preferably in the range of from 2 to 4 hours. The final EPM or EPDM product can contain the following amounts of reacted comonomers: from 35 to 80 percent by weight ethylene; from 18 to 50 percent by weight propylene; and from 0 to 15 percent by weight diene. The crystallinity, also in weight percent based on the total weight of the EPM or EPDM, can be in the range of zero (essentially amorphous) to 15 percent by weight (nearly amorphous). The Mooney viscosity can be in the range of from 10 to 150 and is preferably from 30 to 100. The Mooney viscosity is measured by introducing the EPM or EPDM into a vessel with a large rotor, preheating for one minute at 100°C, and then stirring for four minutes at the same temperature. The viscosity is measured at 100°C in the usual manner. The fluidized bed reactor can be the one described in United States patent 4,482,687 or another conventional reactor for the gas phase production of, for example, polyethylene. The bed is usually made up of the same granular resin that is to be produced in the reactor. Thus, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles, and catalyst particles fluidized by polymerizable and modifying gaseous components introduced at a flow rate or velocity sufficient to cause the particles to separate and act as a fluid. The fluidizing gas is made up of the initial feed, make-up feed, and cycle (recycle) gas, i.e., monomer and, if desired, modifiers and/or an inert carrier gas. A typical cycle gas is comprised of ethylene, nitrogen, hydrogen, and propylene, either alone or in combination. The process can be carried out in a batch or continuous mode, the latter being preferred. The essential parts of the first reactor are the vessel, the bed, the gas distribution plate, inlet and outlet piping, a compressor, a cycle gas cooler, and a product discharge system. In the vessel, above the bed, there is a velocity reduction zone, and in the bed, a reaction zone. Both are above the gas distribution plate. Variations in the reactor can be introduced if desired. One involves the relocation of the cycle gas compressor from upstream to downstream of the cooler and another involves the addition of a vent line from the top of the product discharge vessel (stirred product tank) back to the top of the reactor to improve the fill level of the product discharge vessel. The advantages of the invention are found in improved cure performance; improvement in high temperature crystallinity; the provision of a catalyst system, which is equal to or better than commercially available solution catalyst systems for the production of EPM and EPDM; and good particle morphology. Further, the catalyst system can be advantageously used for the production of polyethylene resins . These polyethylenes are homogeneous, characterized by narrow molecular weight distributions and narrow comonomer distributions. A typical process in which the catalyst system described above can be used can be found in United States patent 4,508,842, which is mentioned above. The catalyst precursor can be used in prepolymer form in polyethylene production just as in EPR production. The preferred temperature for the production of homogeneous polyethylenes is in the range of from 35° C to 85° C. The polyethylenes are, generally, copolymers of ethylene and one or more alpha-olefins having 3 to 12 carbon atoms, and preferably 3 to 8 carbon atoms. Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Typical comonomer molar ratios are as follows: the propylene/ethylene ratio can be in the range of from 0.05 : 1 to 2.5 : 1 and is preferably in the range of from 0.25 : 1 to 1.5 : 1. The 1-hexene/ethylene molar ratio can be in the range of from 0.005 : 1 to 0.050 : 1 and is preferably in the range of from 0.008 : 1 to 0.012 : 1. The invention is illustrated by the following examples. Examples 1 to 12 In the examples, the reactor used for the preparation of the catalyst precursor, the oxidation of the catalyst precursor, the prepolymerization, and the polymerization is a stirred reactor. Both the prepolymerization and the polymerization are carried out in a hexane slurry. The catalyst system for both polymerizations includes a vanadium based catalyst precursor, in pre-oxidized form or not pre-oxidized; a cocatalyst, and, optionally, a promoter. The catalyst precursor is first prepared using conventional procedures such as the procedure described in United States patent 4,508,842, i.e., vanadium trichloride and an electron donor (tetrahydrofuran) are supported on dehydrated silica followed by a modification step to reduce the supported precursor with diethylaluminum chloride (DEAC). The pre-oxidation process using various oxidants is described as follows: (1) Several grams of dry catalyst precursor are placed in an inert atmosphere. A large excess of dry oxygen is passed over the sample until the atmosphere is one of essentially pure oxygen. The sample is maintained in that atmosphere for 60 minutes. It is determined that bulk vanadium oxidation state is +4.3. Note that no diluent is used in this case. (2) 5.0 grams of catalyst precursor ( 2.28 weight percent vanadium; 2.23 millimoles) are placed in a 50 milliliter reactor with 45 milliliters of hexane under nitrogen. Oxygen is added to the system until the atmosphere is essentially 100 percent oxygen. The mixture is stirred for 60 minutes, and is then dried under high vacuum. (3) A prepolymerized catalyst precursor containing 120 grams of polymer (9 percent by weight C3) per gram of catalyst precursor is treated with an excess of essentially pure oxygen for 10 minutes. No diluent is used. (4) 3.0 grams of catalyst precursor (2.28 percent by weight vanadium; 1.34 millimoles) are placed in a 50 milliliter reactor with 50 milliliters of hexane under a nitrogen atmosphere. Five millimoles of nitrobenzene are added slowly. The mixture darkens immediately. The mixture is stirred at 50° C for 30 minutes, and then the solvent is removed under high vacuum. The bulk vanadium oxidation state is greater than +4. (5) 3.0 grams of catalyst precursor (2.28 percent by weight vanadium; 1.34 millimoles) are placed in a 50 milliliter reactor with 35 milliliters of hexane under nitrogen. Perchloropropylene (PCP) (7.0 milliliters as a 1 molar hexane solution) is added. The mixture is stirred for 60 minutes at 50° C. The solvent is removed under high vacuum. That bulk vanadium oxidation state is +3. The catalyst precursor can be used as is or the excess oxidant can be removed with hexane washes. In any case, the bulk vanadium oxidation state remains at +3. In examples 1 to 4, and 7, the precursor is pre-oxidized. In examples 8 and 9, the precursor is not pre-oxidized. Prepolymerization is effected in examples 5 and 6 using the prepolymerized catalyst precursors prepared for those examples. The prepolymerized precursor of example 6 is pre-oxidized while the prepolymerized precursor of example 5 is not. Polymerization is then effected for all of the examples. Prepolymerization A catalyst precursor is prepared, as above, from vanadium trichloride (VCl 3 ), dehydrated silica, and diethylaluminum chloride (DEAC) with a composition of 0.43 millimole of VCl 3 per gram of catalyst precursor, an excess of tetrahydrofuran (THF), and 1.2 millimole of DEAC per gram of catalyst precursor. A reactor, as described above, is charged with 270 milliliters of isopentane followed by 1600 grams of a 20 weight percent solution of TIBA (cocatalyst) in isopentane. The mixture is heated to 50°C for one hour to promote the reaction of the cocatalyst with any water present in the isopentane. After heating is complete, the batch is cooled to below 25°C, 1590 millimoles of DFTCA are added as catalyst promoter, immediately followed by 530 millimoles of catalyst precursor. Prepolymerization is then started by pressuring the reactor to 206.7 kPa (30 psig) with ethylene. Polymerization begins within 5 minutes, as evidenced by the steady feed of ethylene required to maintain the reactor pressure and by an increase in the reaction temperature to 30°C. The reactor pressure is gradually increased to 344.5 kPa (50 psig), and the reaction temperature is gradually increased to 50°C. After sufficient ethylene has been fed to give a theoretical prepolymer loading of 60 grams of polymer per gram of supported catalyst precursor, the feed is then stopped and the remaining monomer in the reactor allowed to react. When the reactor pressure reaches a steady value and the batch has cooled to 30°C, the agitator is shut off, the polymer allowed to settle, and the supernatant liquid removed by a dip tube. Remaining isopentane is removed by heating the batch to 40° C at 0 kPa (0 psig) with a nitrogen sparge. The dried prepolymer is screened through a 20 mesh screen kept inert by a nitrogen purge, and screened prepolymer is collected. In example 11, the prepolymerized catalyst precursor is pre-oxidized as described above. Polymerization To a one liter stirred batch reactor is charged, under nitrogen, 600 milliliters of dry hexane. The catalyst precursor is then charged, followed by a one time batch charge of hydrogen for molecular weight control. The reactor is pressurized to 826.8 kPa (120 psi) at the desired reaction temperature with ethylene and propylene to establish a 1:1 molar ratio gas composition. The ENB is charged next, if used. The initial charge of ENB is 5 milliliters. The promoter is charged and the reactor solution temperature is lowered 5 to 10° C before the addition of the cocatalyst. The cocatalyst is added and the reactor solution is brought up to the desired temperature. Propylene and ethylene are fed at a 0.25 C3/C2 molar ratio so as to maintain reactor pressure at 826.8 kPa (120 psi). ENB, if used, is added as needed to maintain constant concentration in the reactor. At the end of a reaction period of 60 minutes, ethanol is injected into the reaction solution to quench the polymerization reaction. The polymer is isolated by coagalation in methanol followed by filtration. In examples 5 and 6, the polymer contains residual prepolymer. Residual amount of prepolymer and catalyst productivity are determined by mass balance, and the polymer composition is determined by NMR (nuclear magnetic resonance) analysis. Process variables and various properties of the resin product are set forth in the Table. Notes to Examples and Table: 1. DEAC = diethylaluminum chloride TIBA = triisobutylaluminum CHCl 3 = chloroform ETCA = ethyl trichloroacetate DFTCA = difluorotetrachloroethane EASC = ethylaluminum sesquichloride C2 = ethylene C3 = propylene ENB = ethylidene norbornene NB = nitrobenzene PCP = perchloropropene or perchloropropylene mmol = millimole EPDM = ethylene/propylene/ethylidene norbornene terpolymer rubber. 2. Pre-oxidation process = See above processes (1) to (5), above. 3. Cat Prod(g/mmol V/hr) = the grams of EPDM produced per millimole of vanadium per hour. 4. Flow Index(g/10 min) = flow index is determined under ASTM-1238, Condition F, at 190° C and 21.6 kilograms. 5. MOONEY (EST ODR) = Mooney viscosity is estimated using an oscillating disk rheometer (ODR). It is estimated from a linear correlation of gum Mooney viscosity under standard conditions [M(L)(minimum torque resistance) 1+4 at 125° C] with M(L) measured in ASTM D-3568 formula no. 1 using an ODR at 160° C and a 1° arc at 100 cpm. 6. Cure: M(H) minus M(L) = Formula no. 1 of ASTM D-3568 is used following Procedure 6.1.2 for a miniature internal mixer and Practice D-3182. A Brabender™ mixer with a mixing head maintained at 90° C is used. Vulcanization characteristics are measured following ASTM D-2084 test methods for the ODR. The cure meter test cavity is maintained at 160° C. The disk is oscillated through a 1° arc rotational amplitude at 100 cpm. The force required to rotate the disk to maximum amplitude is continuously measured. The difference between the maximum torque resistance, M(H), and M(L) is recorded. 7. Examples 3, 5, 8, and 9 are comparative examples. Example 3, using a TIBA cocatalyst and a chloroform promoter, has a very low catalyst productivity value. Example 5 (using the prepolymerized precursor, which is not oxidized) produces an EPDM with just a satisfactory cure value. Cure values of less than 20 are considered poor; cure values from 20 to 25 are considered satisfactory; and cure values above 25, especially above 30, are considered excellent. Example 8 has poor diene incorporation as shown by the percent by weight of ENB in the product, and a poor cure value. Example 9 has improved diene incorporation, but just a satisfactory cure value.

Claims: A process for the production of EPRs comprising contacting ethylene, propylene, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX 3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX 3 is soluble; (ii) a modifier having the formula BX 3 or AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is as defined above; and a is 1 or 2; and (iii) a support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with an oxidant in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) a cocatalyst consisting essentially of a compound having the formula AlR (3-a) X a and, optionally, a compound having the formula AlR 3 wherein R, X, and a are as defined above; and, (C) optionally, a promoter, which is a chlorinated ester having at least 2 chlorine atoms; a saturated or unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms; or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms. A process as claimed in claim 1 wherein the catayst precursor or prepolymerized catalyst precursor has been preoxidized with at least one mole of oxidant per gram atom of vanadium. A process as claimed in claim 1 or claim 2 wherein the oxidant is oxygen, nitrobenzene, perchloropropene, or trichlorotoluene. A process as claimed in any one of the preceding claims which is carried out in the gas phase in a fluidized bed. A process as claimed in claim 1 for the production of EPR's comprising contacting ethylene, propylene, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of VCl 3 and tetrahydrofuran; (ii) a modifier, which is diethylaluminum chloride or ethylaluminum sesquichloride; and (iii) a silica support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with oxygen or perchloropropene in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) as a cocatalyst, diethylaluminum chloride or a mixture of diethylaluminum chloride and triethylaluminum; and (C) optionally, as a promoter, ethyl trichloroacetate. A process as claimed in claim 5 which is carried out in the gas phase in a fluidized bed. A catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX 3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX 3 is soluble; (ii) a modifier having the formula BX 3 or AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is as defined above; and a is 1 or 2; and (iii) a support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with an oxidant in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) a cocatalyst consisting essentially of a compound having the formula AlR (3-a) X a and, optionally, a compound having the formula AlR 3 wherein R, X, and a are as defined above ; and, (C) optionally, a promoter, which is a chlorinated ester having at least 2 chlorine atoms; a saturated or unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms; or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms. A catalyst system as claimed in claim 7 comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of VCl 3 and tetrahydrofuran; (ii) a modifier, which is diethylaluminum chloride or ethylaluminum sesquichloride; and (iii) a silica support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with oxygen or perchloropropene in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) as a cocatalyst, diethylaluminum chloride or a mixture of diethylaluminum chloride and triethylaluminum; and (C) optionally, as a promoter, ethyl trichloroacetate. A process for the production of homogeneous polyethylene comprising contacting a mixture comprising ethylene and one or more alpha-olefins, under polymerization conditions, with a catalyst system comprising: (A) a catalyst precursor comprising: (i) a vanadium compound, which is the reaction product of (a) VX 3 wherein each X is independently chlorine, bromine, or iodine; and (b) an electron donor, which is a liquid, organic Lewis base in which VX 3 is soluble; (ii) a modifier having the formula BX 3 or AlR (3-a) X a wherein each R is independently alkyl having 1 to 14 carbon atoms; each X is as defined above; and a is 1 or 2; and (iii) a support for said vanadium compound and modifier, said catalyst precursor being in an independent or prepolymerized state, wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with an oxidant in an amount sufficient to increase the oxidation state of the vanadium by at least one; (B) a cocatalyst consisting essentially of a compound having the formula AlR (3-a) X a and, optionally, a compound having the formula AlR 3 wherein R, X, and a are as defined above; and, (C) optionally, a promoter, which is a chlorinated ester having at least 2 chlorine atoms; a saturated or unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms; or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms. A process as claimed in claim 9 which is carried out in the gas phase in a fluidized bed.

Inventors: CANN KEVIN JOSEPH, CANN, KEVIN JOSEPH
Applicants: UNION CARBIDE CHEM PLASTIC, UNION CARBIDE CHEMICALS & PLASTICS TECHNOLOGY CORPORATION
Application year: 1994
Main classification: C08F210
IPC codes: C08F2, C08F210, C08F10, C08F4